Field Of The Invention
This invention relates in general to a sewing machine, and in particular to a new and useful machine having a drive for a presser.
In zig zag sewing machines, both the press foot and the needle plate are usually provided with a slotlike sewing hole, the dimensions of which, transverse to the direction of feed of the sewing material are determined by the maximum cross stitch width. Such large sewing holes are a disadvantage, since the sewing material can only inadequately be supported against the forces exerted by the needle at the site of formation of the stitch.
It is common in such sewing machines to adapt the size of the sewing hole to the type of stitch being executed. The needle plate of the familiar sewing machine from U.S. Pat. No. 4,303,028 has a slotlike sewing hole, the dimensions of which transverse to the direction of feed, of the sewing material, can be reduced by a relatively cumbersome controlling unit after adjusting the machine to a straight stitch. In this case, no individual adaptation of the size of the sewing hole to rather small cross stitch widths is provided, nor even possible.
Since the sewing hole of the particular press foot which is installed cannot be altered by the aforesaid controlling unit, either the press foot provided for zig zag stitches must be used to produce straight stitches, or the press feet must be changed with the type of stitch. This gives rise to the danger that, by mistaken handling of the zig zag mechanism, the stitch forming unit and the sewing hole of the needle plate will be converted to a zig zag stitch, but it will be forgotten to change the press foot provided for straight stitch. This might cause damage to the press foot, as well as to parts of the stitch forming unit.
U.S. Pat. No. 4,303,082 describes a further modification of such arrangement, whereby the press foot corresponding to the type of stitch used on each occasion correspondingly activates both the zig zag mechanism and the controlling unit for the needle plate. This modification, as well, requires a time consuming changing of the press foot to change the type of stitch.
From Japanese declaration No. 49-9491, a holder used to carry a press foot is fastened to the needle bar. The press foot is carried in a bearing block, likewise fastened to the needle bar, whereby this simultaneously acts as an abutment for the pressing spring. By this arrangement, the entire pressing mechanism takes part in the transverse movements of the needle bar, so that the moment of inertia of the latter is significantly increased.
Since the press bar in this arrangement is always raised along with the needle bar, and the needle bar moves backward against the force of the pressing spring, a relatively large force is needed to actuate the needle bar. Furthermore, the supporting of the sewing material by the press foot when the needle emerges is not optimal, since the pressing spring is at least partly relieved of tension by the raising of the needle bar.